Radioactive dating of rock samples
This has to do with figuring out the age of ancient things.
If you could watch a single atom of a radioactive isotope, U-238, for example, you wouldn’t be able to predict when that particular atom might decay.
However, the crater number relation must be calibrated against something with a known age.
To measure the passage of long periods of time, scientists take advantage of a regularity in certain unstable atoms.
It might take a millisecond, or it might take a century. But if you have a large enough sample, a pattern begins to emerge.
It takes a certain amount of time for half the atoms in a sample to decay.
Since the 1950s, geologists have used radioactive elements as natural "clocks" for determining numerical ages of certain types of rocks. "Forms" means the moment an igneous rock solidifies from magma, a sedimentary rock layer is deposited, or a rock heated by metamorphism cools off.
Recall that an isotope is a particular form of an element.Or you can tell that certain parts of the Moon's surface are older than other parts by counting the number of craters per unit area.The old surface will have many craters per area because it has been exposed to space for a long time. If you assume that the impact rate has been constant for the past several billion years, then the number of craters will be proportional to how long the surface is exposed.This decay is an example of an exponential decay, shown in the figure below.Knowing about half-lives is important because it enables you to determine when a sample of radioactive material is safe to handle.